Center tap transformer

hhsting

Senior Member
Why buy, wire, and pay forever to heat three sets of windings when you only need one set?
I am not the designer and I cannot enforce this on designer. Been asking the same question to the designer why go with delta center tap transformer and he just goes on loops without answering question.

One reason could be voltage drop 480V three phase versus 480V single phase. The transformer primary feeder is at bottom basement of building and transformer sits on penthouse roof 200 feet up.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
One reason could be voltage drop 480V three phase versus 480V single phase.
I think the proper compensation would be to upsize two conductors, and would likely cost less.

Its for cell tower site which mainly feeds 2 poles 240V single phase 2 rectifiers, 240V surge, and 120V single phase 2 receptacles, 2 AC power alarms
If you end up with a 3ph transformer anyway, suggest using a 3ph panel, and putting the rectifiers on the high leg, one on each non-tapped secondary, and the rest on the center-tapped secondary, also evenly divided.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
Its for cell tower site which mainly feeds 2 poles 240V single phase 2 rectifiers, 240V surge, and 120V single phase 2 receptacles, 2 AC power alarms
In principal, this set of loads could use all three phases. In general, 240V single phase devices can be connected across any of the delta legs to get 240V.

It is possible that the designer had planned this 3 phase distribution, equipment was purchased, and then some aspect of the equipment restricted them to the 240V midpoint grounded leg.

The things called 'rectifiers' are really most likely AC input DC output switching power supplies which _should_ be able to connect across any of the 240V terminals but might have a restriction to the grounded leg.

-Jon
 

hhsting

Senior Member
Found out. They have very old switchboard and it came with 3 pole spares only. So they have to have three phase on primary side since they are feeding from switchboard. I just done see why 3 pole breaker in switchboard be replace with 2 pole breaker?
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Found out. They have very old switchboard and it came with 3 pole spares only. So they have to have three phase on primary side since they are feeding from switchboard. I just done see why 3 pole breaker in switchboard be replace with 2 pole breaker?
As long as the existing breaker is of suitable rating, use any two poles.
 
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